The present invention relates to a relative linear motion apparatus in which a second structure is movable in linear motion relative to a first structure, for example in which the second structure formed like a plate is put in the first structure formed like a frame, plurality of rectilinear guides are arranged between the first structure and the second structure so that the second structure is movable relative to the first structure.
In a known art, the Japanese Patent Laid-open Publication No. HEI 7-190053 discloses a mounting plate for a rectilinear guide in order to allow misalignment such as an installation error caused when rectilinear guide is installed. FIG. 15 shows this mounting plate. The mounting plate 1 is put between the rectilinear guide 5 and a fixed member 2, and allows the rectilinear guide 5 to move in a perpendicular direction {circle around (1)} against the fixed member 2. The mounting plate 1 consists of fixed portion 6 mounted to the fixed member 2, attached portion 4 mounted to a movable block 3 of the rectilinear guide 5, and thin board portion 7 which connect the fixed portion 6 with the attached portion 4.
Since the misalignment such as the installation error deforms the thin board portion 7, the attached portion 4 moves relative to the fixed portion 6 in the perpendicular direction {circle around (1)} and the mounting plate 1 absorbs the misalignment.
In some cases, a relative linear motion apparatus comprises a fixed member (first structure) having at least a pair of inner wall surfaces opposing to each other, a movable member (second structure) arranged between the pair of inner wall surfaces, two rectilinear guides arranged between the fixed member and the movable member. The movable member guided by the rectilinear guides slides relative to the fixed member in linear motion to a direction parallel to the inner wall surfaces of the fixed member.
In such a relative linear motion apparatus, when the parallelism of one rectilinear guide to the other rectilinear guide is spoiled by an installation error, or when installing position for the rectilinear guide is under slight error, the movable member can not slide smoothly. Therefore it is necessary to install the rectilinear guides with high accuracy. Also, even if the rectilinear guides are installed with high accuracy, since the rectilinear guides are applied a load caused by thermal expansion and contraction difference between the fixed member and the movable member in a perpendicular direction to the wall, the movable member sometimes can not slide smoothly
In case the conventional mounting plate 1 is used for the relative linear motion apparatus described above, deformation of the thin board portion 7 is small and the mounting plate 1 can not absorb a large error. Therefore, though the mounting plate 1 can absorb small misalignment, the mounting plate 1 can not sufficiently absorb thermal expansion and contraction difference between the fixed member and the movable member.
Also the conventional mounting plate 1 allows the movable member to move slightly not only in the perpendicular direction {circle around (1)} but also in a horizontal direction {circle around (2)} (which is parallel to the inner wall surface and perpendicular to a sliding direction of the movable member). So the movable member can not be guided with good rigidity. Further, it is difficult to process the thin board portion 7 on the mounting plate 1.
An object of the present invention is to provide a relative linear motion apparatus which can sufficiently absorb the installing error of rectilinear guides or thermal expansion and contraction difference between the fixed member and the movable member, and guide the movable member with good rigidity.
In order to achieve the above-mentioned object, the relative linear motion apparatus according to the present invention is constructed so as to comprise: a first structure having at least a pair of inner wall surfaces opposing to each other; a second structure arranged between the pair of inner wall surfaces, the second structure being movable in linear motion relative to the first structure; at least two rectilinear guides arranged between the first structure and the second structure; and a displacement absorbing device arranged on at least one of the first structure and the second structure so as to allow at least one of the two rectilinear guides to move in a intersecting direction against the wall surfaces. The two rectilinear guides make the second structure to be movable in linear motion relative to the first structure.
When the second structure is arranged between the pair of inner wall surfaces of the first structure through the rectilinear guides, and a processing error including an installation error or thermal expansion and contraction difference between the first structure and the second structure occurs, the second structure could not smoothly slide relative to the first structure.
According to the invention described above, even if the processing error including the installation error occurs, or even if the thermal expansion and contraction difference occurs, the displacement absorbing device can absorb the displacement of the rectilinear guide in the intersecting direction against the wall surfaces. Therefore the rectilinear guides are not applied an excessive load and work smoothly, and the second structure smoothly slide relative to the first structure. If the displacement absorbing device allows at least one of the two rectilinear guides to move only in the intersecting direction against the wall surfaces (for example only in the perpendicular direction to the wall surfaces), and restricts the rectilinear guide to move in a horizontal direction (which is parallel to the inner wall surface and perpendicular to a sliding direction of the second structure), it is possible to guide the second structure with good rigidity.
In the relative linear motion apparatus to which the present invention is applied, at least one of the two rectilinear guides moves in the intersecting direction against the wall surfaces due to a processing error including an installation error caused when said at least one of the two rectilinear guides is installed or thermal expansion or thermal contraction difference between the first structure and the second structure.
The relative linear motion apparatus of the invention is effective in absorbing such large displacement.
In a preferred embodiment of the present invention, the displacement absorbing device is arranged between (i) one of said first structure and said second structure and (ii) one of said two rectilinear guides, said displacement absorbing device having an elastic beam which can deflect toward the intersecting direction against the wall surfaces.
According to this embodiment, an elastic beam can deflect and absorb the processing error or the thermal expansion and contraction difference between the first structure and the second structure.
In a further embodiment, said elastic beam has span which is capable of deflection, and the span is longer than width of said one of the two rectilinear guides.
According to this embodiment, the span of the elastic beam become longer, and the deflection of the elastic beam become larger. Therefore the elastic beam can absorb the large processing error or the large thermal expansion and contraction difference.
In a further embodiment, a spacer is arranged between said elastic beam and said one of the two rectilinear guides so that said elastic beam deflects larger, the spacer having width less than the width of said one of the two rectilinear guides.
According to this embodiment, since the load placed on the elastic beam approaches to concentrated load from distributed load, the elastic beam deflects larger.
In a further embodiment, said elastic beam has both longitudinal end portions fixed to said first structure or said second structure, and said one of the two rectilinear guides is arranged in the middle of said elastic beam in a longitudinal direction thereof.
According to this embodiment, the elastic beam deflects with easy construction.
In a further embodiment, said first structure or said second structure has guide surfaces which guide said one of the two rectilinear guides to move in the intersecting direction against the wall surfaces.
According to this embodiment, since the rectilinear guide is guided to move in the intersecting direction against the wall surfaces, the rectilinear guide is prevented from moving in another direction except the intersecting direction. For example it is possible for the rectilinear guide to move only in the perpendicular direction to the wall surfaces so as to absorb the error and not to move in the horizontal direction. Therefore the second structure can be guided with good rigidity.
In a further embodiment, said guide surfaces allows said one of the two rectilinear guides to move only in a perpendicular direction to the wall surfaces without occurrence of change in posture thereof.
According to this embodiment, the rectilinear guide is allowed to move only in the perpendicular direction to the wall surfaces, and is restricted to move in the horizontal direction.
In a further embodiment, each of said rectilinear guides comprises:
a track member formed with a rolling member rolling surface along a longitudinal direction;
a movable block mounted to be relatively movable to the track member formed with a rolling member circulation passage including a loaded rolling member rolling surface opposing to the rolling member rolling surface of the track member when mounted;
and a number of rolling members arranged in the rolling member circulation passage so as to circulate therein in conformity with the relative motion of the movable block with respect to the track rail.
In a further embodiment, each of movable blocks is fixed to said each of said inner wall surfaces of said first structure, and each of track members is fixed to each of edges of said second structure.
In a further embodiment, said track member is integrally formed with said second structure by an inserting mold.
In case the second structure is arranged between the pair of the inner wall surfaces of the first structure through the rectilinear guides, it is necessary to reduce the processing error including the installation error so that the second structure smoothly slides relative to the first structure.
According to this embodiment, since the track rail is inserted in second structure and is integrally molded with the second structure, the processing error is reduced as small as possible. Also, since component parts are reduced too, a relative linear motion apparatus of the invention can be fitted for mass production. On the contrary, if the track rail and the second structure are separately made and the track rail and the second structure are joined together with bolts and so on, the occurrence of the installing error caused by the operator""s degree of aging can not be avoided.